Cellulose capsules

ABSTRACT

A method for making an oil-in-water dispersion or water-in-oil dispersion is disclosed. The method comprises the step of mixing a hydrophilic medium, a hydrophobic composition and non-derivatized cellulose solution in an ionic liquid.

FIELD OF INVENTION

A composition having an interior hydrophobic space encapsulated by atleast one non-derivatized cellulose molecular layer surrounded by ahydrophilic medium and methods for hydrolyzing cellulose and making anoil-in-water dispersion or water-in-oil dispersion, are provided.

BACKGROUND OF THE INVENTION

Encapsulation is a process in which tiny particles or droplets aresurrounded by a coating to impart many useful properties to smallcapsules. In a relatively simplistic form, a microcapsule is a smallsphere with a uniform wall around it. The material inside themicrocapsule is referred to as the core, internal phase, or fill,whereas the wall is sometimes called a shell, coating, or membrane. Mostmicrocapsules have diameters between a few microns to a few millimeters.The core may be a crystal, a jagged adsorbent particle, an emulsion, asuspension of solids, or a suspension of smaller microcapsules. Themicrocapsule even may have multiple walls. The reasons formicroencapsulation are countless. In some cases, the core must beisolated from its surroundings, as in isolating vitamins from thedeteriorating effects of oxygen, retarding evaporation of a volatilecore, improving the handling properties of a sticky material, orisolating a reactive core from chemical attack. In other cases, theobjective is not to isolate the core completely but to control the rateat which it leaves the microcapsule, as in the controlled release ofdrugs or pesticides. The problem may be as simple as masking the tasteor odor of the core, or as complex as increasing the selectivity of anadsorption or extraction process.

The technique of microencapsulation depends on the physical and chemicalproperties of the material to be encapsulated: complex coacervation,centrifugal extrusion, vibrational nozzle, spray-drying, interfacialpolycondensation, interfacial cross-linking, in-situ polymerization,etc.

The efforts towards thermal energy storage (TES) and sustainable energytechnologies have been intensified over the past decades. Phase changematerials (PCMs) can be directly used or consumed as a component of thecomposite-like energy storage materials (ESM) in TES applications likesolar energy utilization, energy conserving in buildings, thermalinsulation, thermal adaptable textile materials, etc. because they allowlarge amounts of heat to be stored during their melting and to bereleased during their solidifying process. A phase-change material is asubstance with a high heat of fusion which, melting and solidifying at acertain temperature, is capable of storing and releasing large amountsof energy. Heat is absorbed or released when the material changes fromsolid to liquid and vice versa; thus, PCMs are classified as latent heatstorage (LHS) units. Micron size dispersion of PCMs in the form ofmicroparticles, microcapsules or PCM impregnated into open-cellfoam-like supporting material make them more usable than the traditionalblock PCM because of: (i) protecting the PCM against the influences ofthe outside environment, (ii) increasing the heat-transfer area, (iii)permitting the core PSM to withstand changes in volume, as the phasechange occurs and allowing small and portable TES system.

Many types of PCMs such as salt hydrates, paraffins, and fatty acidshave been investigated. Among the studied PCMs, paraffins (alkanes) havebeen often used as a latent heat energy storage material (LHESM) withthe advantages of high enthalpy of phase change, small segregation ofcomponents, small changes in structure and volume during repeated phasetransitions (less than 10 v/v %), negligible super- and sub-cooling, lowvapor pressure, self-nucleating behavior, very few safety constraints,high chemical stability, insolubility in water, biocompatibility, goodrecyclability and low cost. They have attractive thermal properties fordifferent applications such as thermal adaptable fibers, thermalinsulation building materials, heat exchangers in air conditioning andwater heating systems.

The supporting material in the composite-like ESM is often made ofhigh-density polyethylene or polypropylene, polyacrylamide, ceramics,silica powder or wood fiberboards, poly(methyl methacrylate),poly(ethylene oxide), poly(ethylene terephthalate), silkfibroin-chitosan.

Since PCMs transform between solid to liquid and vice versa in thermalcycling, encapsulation naturally become the obvious storage choice.Other than the form stability and leakage resistance microencapsulatedbulk PCMs promise additional advantages: (i) no need for additionalstorage container, thus reducing the cost of TES systems; (ii)minimizing the thermal resistance caused by PCM storage container; (iii)easily fabricated in desired shapes and dimensions; (iv) possibility tocut the ECM into arbitrary shapes without leakage. Most of the above ESMcomposites are prepared by immersing of the micronized PCM intosupporting material by its direct incorporation at the mixing stage ofmaterial production.

Additional wide application field of PCMs is the fluid pipingheat-transfer systems. In such conventional systems, thermal energy istransferred by the sensible heat of a single-phase working fluid, beingproportional to the source/sink temperature difference. Because thesystems are often operated with small temperature differences, thesingle-phase fluid must be pumped at a high-volume flow rate. As aresult, the system consumes a large amount of pumping power. The use ofPCM particles suspended in a single-phase working fluid (making socalled slurry) provides additional thermal capacity from the latent heatassociated with the solid/liquid phase change. This enhancement is dueto a combination of four factors: (i) the often higher thermalconductivity of the added particles, (ii) the increased microconvectiondue to the particles, (iii) a higher effective specific heat during thephase change process and, (iv) the greater temperature difference thatis maintained as the phase change material melts/solidifies. The mainmerits of usage the microcapsulated PCM slurries are as follows: (i) thephase change temperature range could be well fitted for purposes of aspecific system by properly selecting the PCM, (ii) the slurry particlesize can be very small, which results in smaller frictional pressureloss for the same mass flow rate and less risk of clogging thetransportation pipes, (iii) the extremely sharp viscosity decreasing inthe bimodal diameter distribution dispersions, which sufficientlyincreases the pumping efficiency of the concentrated slurries.

It was found that nonencapsulated PCMs are sticky and can glue togetherto form large lumps; clogging often occurs in a piping system, resultingin failure to circulate the slurry through the system, so PCMencapsulation are recently widely used. The small (units of microns orless) PCM capsules were found a very stable during pumping, repeatedcirculations through a slurry flow circuit and multiply thermal cyclingacross the PCM melting temperature, therefore, this type of slurry canbe treated as a conventional single-phase working fluid.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a compositionconsisting or comprising an interior hydrophobic space encapsulated byat least one non-derivatized cellulose molecular layer, wherein thecellulose is surrounded by a hydrophilic medium

In a further embodiment, the present invention provides a compositionconsisting or comprising an interior hydrophilic space encapsulated bynon-derivatized cellulose molecular layer, wherein the cellulose issurrounded by a hydrophobic medium.

In a further embodiment, the present invention provides a compositionconsisting or comprising capsules in a hydrophilic medium, wherein thecapsules having an interior hydrophobic space separated from thehydrophilic medium by at least one layer consisting non-derivatizedcellulose.

In a further embodiment, the present invention provides a compositionconsisting or comprising capsules in a hydrophobic medium, wherein thecapsules have an interior hydrophobic space separated from thehydrophobic medium by at least one layer consisting non-derivatizedcellulose. In one embodiment, a composition as described herein isdevoid of a surfactant. In one embodiment, a composition as describedherein is oil-in-water composition. In one embodiment, a composition asdescribed herein is water-in-oil composition.

In a further embodiment, the present invention provides a method formaking an oil-in-water dispersion or water-in-oil dispersion, comprisingthe step of mixing a hydrophilic medium, a hydrophobic composition andnon-derivatized cellulose solution in an ionic liquid.

In a further embodiment, the present invention provides a method forobtaining a solid-state, stable, dispersion of the composition asdescribed herein by simply drying the composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. A graph showing the electrical conductivity of dispersion as afunction of the relative volumetric water content (IL means more than95% vol. ionic liquid, H₂O means less than 1% vol. of IL in solvent).The top axis indicates the time required to achieve the correspondingconductivity during dialysis against pure water.

FIG. 2. A graph showing the X-ray diffraction patterns of pure eicosaneat 20° C. (1) and at 60° C.

FIG. 3. A graph showing the X-ray diffraction patterns of driedeicosane/cellulose dispersion (1) and pure eicosane (2) at 60° C.

FIG. 4. A graph showing the X-ray diffraction patterns of amorphouscellulose, maid following [R. Avolio, I. Bonadies, D. Capitani, M. E.Errico, G. Gentile, M. Avella Carbohydrate Polymers 87 (2012) 265] (1),initial microcrystal cellulose (crystalline cellulose I) (2) andcrystalline cellulose II (3) [D. L. Kaplan, Biopolymers From RenewableResources. Berlin, Springer Verlag, Berlin, 1998.]

FIGS. 5A, 5B and 5C. A photograph showing the differenteicosane/cellulose (4:1) dispersion samples: 6 wt. % microcapsulatedwater based dispersion (a); this dispersion dialyzed against 20 wt. %aqueous PEG solution for 24 hours followed by oven desiccation for 4hours at 60° C. (sample mass 2.2 g) (b); dispersion concentrate, blownin vacuum oven at 60° C. (sample mass 0.4 g) (c).

FIG. 6. Is a graph showing the particle size distribution ofrepresentative cellulose coated eicosane dispersion (eicosane/celluloseratio 4:1) in water: native dispersion (solid line) and re-dissolveddispersion (dotted line).

FIGS. 7A, 7B and 7C. Is a micrograph showing Cryo-TEM images ofvitrified thin films of the aqueous dispersions: eicosane-containingparticles vitrified before core crystallization (at 60° C.) (a),paraffin oil-containing particles vitrified at 20° C. (b),heptane-containing particles vitrified at 20° C. (c).

FIGS. 8A and 8B. Is a micrograph showing Cryo-TEM image of the aqueouseicosane-containing dispersion vitrified after core crystallization atambient temperature. (a) image taken at low electron dose, (b) same areaafter electron irradiation at about 3000 e/nm2, arrow indicates theradiation stable shell.

FIG. 9. Is a micrograph showing HR-SEM imaging of the cryo-fracturedsurface of the eicosane based sample. Inset: a higher magnificationimage of area where the fracture cut across the particles.

FIGS. 10A and 10B. Is a micrograph showing structures obtained afterblowing of different dispersions: eicosane/cellulose (a);heptane/cellulose (b).

FIG. 11. Is a graph showing the pH dependence of the ζ-potential ofcellulose coated eicosane dispersion.

FIG. 12. Is a graph showing the Differential scanning calorimetry ofpure eicosane (1), eicosane/cellulose (4:1) solid dispersion (2) and 6wt. % aqueous suspension, re-dispersed from solid dispersion (3).

FIG. 13. Is a graph showing the TGA (dotted line) and DTG (solid line)of the solid eicosane/cellulose (4:1) microcapsules.

FIGS. 14A, 14B and 14C. Is a graph showing wide-angle (a) andsmall-angle (b, c) X-ray diffraction patterns from the dried and aqueouseicosane/cellulose (4:1) dispersions. In (a): pure eicosane at ambienttemperature (1), dried dispersion, heated to 60° C. (2), drieddispersion at ambient temperature (3) and dried non-derivatizedcellulose hydrogel (4). In (b): 1—pure eicosane, 2—dried dispersion,3—pure microcrystal cellulose, 4—blown dispersion. In (c): 1-6 wt. %dispersion in IL/water (1:4) solution, 2-12 wt. % aqueous dispersionfrom the repeatedly dissolved solid dispersion.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides the use of pure microcrystallinecellulose as an encapsulating agent. Pure microcrystalline encapsulatesaccording to the invention hydrophobic or oily substances orcompositions. The addition of pure microcrystalline cellulose to oil inwater or water in oil compositions forms hydrophobic/oil core surroundedby a layer or layers of pure microcrystalline that are furthersurrounded by a hydrophilic solution such as an aqueous solution.

In another embodiment, provided herein a composition consisting orcomprising an interior hydrophobic space encapsulated in non-derivatizedcellulose, wherein the cellulose is surrounded by a hydrophilic mediumand a method for making the same. In another embodiment, provided hereina composition consisting or comprising capsules in a hydrophilic medium,wherein the capsules have an interior hydrophobic space separated fromthe hydrophilic medium by at least one layer consisting non-derivatizedcellulose. In another embodiment, provided herein a compositionconsisting or comprising capsules in a hydrophobic medium, wherein thecapsules have an interior hydrophobic space separated from thehydrophobic medium by at least one layer consisting non-derivatizedcellulose. In another embodiment, provided herein a compositionconsisting or comprising a pure non-derivatized cellulose hydrogel orhydrogel capsule.

In some embodiments, the composition described herein is devoid of asurfactant. In another embodiment, provided herein a compositionconsisting capsules in a hydrophilic medium, the capsules having aninterior hydrophobic space separated from the hydrophilic medium by atleast one layer consisting non-derivatized cellulose.

In another embodiment, cellulose in its unmodified form is utilized as anovel emulsifier for formation oil-in-water or water-in-oil dispersionsbased on encapsulation. In another embodiment, cellulose in itsunmodified form is underivatized cellulose. In another embodiment, drieddispersions of hydrophobic compounds encapsulated by cellulose arereadily regenerated by re-dissolution in water. In another embodiment,blowing of damp dispersions yields nanoporous cellulose foam(aerocellulose). In another embodiment, cellulose-encapsulated eicosanedispersions in solid or liquid form possess high effectiveheat-absorption capacity. In another embodiment, the encapsulatingcellulose shell promotes the emergence of an irregular crystallinestructure of the core material.

If the contact angle of water with a compound is less than 30°, thecompound is designated hydrophilic since the forces of interactionbetween water and the compound's surface nearly equal the cohesiveforces of bulk water, and water does not cleanly drain from the surface.If water spreads over a surface, and the contact angle at the spreadingfront edge of the water is less than 10°, the compound is oftendesignated as superhydrophilic provided that the compound's surface isnot absorbing the water, dissolving in the water or reacting with thewater. On a hydrophobic surface, water forms distinct droplets.

As the hydrophobicity increases, the contact angle of the droplets withthe surface increases. Compound's surfaces with contact angles greaterthan 90° are designated as hydrophobic. The theoretical maximum contactangle for water on a smooth surface is 120°. Microtextured ormicro-patterned surfaces with hydrophobic asperities can exhibitapparent contact angles exceeding 150° and are associated withsuperhydrophobicity and the so-called “lotus effect.

The term “hydrophilic”, in some embodiments, refers to molecules thattypically have polar groups. The term “hydrophobic”, in someembodiments, refers to molecules that are typically free of polargroups. In some embodiments, the boundary between hydrophobicity andhydrophilicity occurs when the difference between the apolar attractionand the polar repulsion between molecules or particles of materialimmersed in water is equal to the cohesive polar attraction between thewater molecules. Under these conditions, the interfacial free energy ofinteraction between particles of a material, immersed in water (ignoringelectrostatic interactions), ΔG^(IF), is exactly zero. When the ΔG^(IF)is positive, the interaction of the material with water dominates andthe surface of the material is hydrophilic; when ΔG^(IF) is negative,the polar cohesive attraction between the water molecules dominates andthe material is hydrophobic. Thus, the sign of ΔG^(IF) defines thenature of the surface and the magnitude of ΔGIF and is used, in someembodiments, as the natural quantitative measure of the surfacehydrophobicity or hydrophilicity.

In another embodiment, an interior hydrophobic space is the core or thenucleus of a capsule of the invention which comprises a hydrophobicmaterial such as but not limited to a hydrocarbon. In anotherembodiment, an interior hydrophobic space comprises the hydrophobicinteracting groups of underivatized cellulose.

In another embodiment, underivatized cellulose of the inventioncomprises up to 40% impurities. In another embodiment, underivatizedcellulose of the invention comprises up to 35% impurities. In anotherembodiment, underivatized cellulose of the invention comprises up to 30%impurities. In another embodiment, underivatized cellulose of theinvention comprises up to 25% impurities. In another embodiment,underivatized cellulose of the invention comprises up to 20% impurities.In another embodiment, impurities are organic impurities. In anotherembodiment, impurities include: lignin, hemicellulose, etc.

In another embodiment, an interior hydrophilic space is the core or thenucleus of a capsule of the invention which comprises a hydrophilicmaterial such as but not limited to an aqueous solution. In anotherembodiment, an interior hydrophilic space comprises the hydrophilicinteracting groups of underivatized cellulose.

In another embodiment, a medium is the solution which surrounds acapsule of the invention. In another embodiment, a medium is thesolution which interacts with the outer surface of a capsule of theinvention.

Encapsulated ESMs are generally synthesized with melamine-formaldehyde,urea-formaldehyde or gelatin-formaldehyde as the shell materials.However, formaldehyde is harmful to the health, the remnant of whichshould be reduced to meet the limitation by the medical standards, inparticular, when ESM intends to use for textile.

The present invention provides for the first time the non-derivatizedcellulose hydrogel or solution were used as a novel eco-friendlyemulsifying agents for producing stable oil-in-water or water-in-oildispersions.

When the cellulose/IL solution or cellulose hydrogel were added to theagitated hydrocarbon dispersion in water (oil-in-water), or to waterdroplets dispersed in agitated hydrocarbon (water-in-oil), stabledispersions were, surprisingly, obtained without use of any additionalsurfactant. The control experiments, i.e. physical mixtures ofcellulose/IL solution and water as well as hydrocarbons/IL dispersionand water, did not yield any stable dispersion but exhibited coagulatedcellulose hydrogel in the first case or instantaneous phase separationin the second.

In some embodiments, an interior hydrophobic space consists or comprisesalkanes. In some embodiments, alkanes are used as the core material ofESMs due to their stable chemical properties, suitable thermalproperties and low cost. In some embodiments, cellulose in its ionicliquid solutions is precipitated at room temperature by addition ofwater, methanol, ethanol, acetone etc., forming, hydro-alco-, acetono-and other cellulose lyogels, respectively. It was surprising andunforeseeable for the skilled worker that previously described process,without the use of any surfactants, leads to instant spontaneousemergence of the suspension, consists of alkanes encapsulated intocellulose shell.

Unlike known microfluidic methods of the production of cellulosecapsules, the present process does not require special equipment and theindividual attention of maker to every elaborated capsule. The cellulosecapsules can have different diameter (from tens of nanometers tomillimeters) with small dispersion of dimensions and controllable shellthickness. The novel ESM suspension has an immanent relatively highelectroconductivity, which opens new wide fields of its use.

The novel method for encapsulation of materials in cellulose shellsgives the possibility to obtain the novel “green” materials in thenumerous fields of applications. The suggested process demands thenon-expensive, non-harmful, non-dangerous and easy recyclable andbiodegradable intermediate materials.

The novel, highly stable nano/micro-scale slurries, based on celluloseencapsulated PCMs, have a relatively low viscosity at highconcentrations, which increases their pumping efficiency and permits toincrease the slurry concentration up to 45 wt. %, that allows to enlargethe efficiency of thermal energy transfer systems. Producing theslurries with bimodal particle size distribution also allows sufficientdecreasing the slurry viscosity. The novel solid ESMs have the abilityto maintain the shape and mechanical properties (form stability) andhave no any leakage of melted PCM during phase change process.

The novel cellulose shells have high elastic strength, excellent waterand good fire resistance and very low chemical reactivity. The novel ILbased electroconductive PCM slurry makes it possible to use it inelectrical induction heating loops and could be easily pumped using ofmagnetohydrodynamic pumps in the compact thermal exchange systems.

Moreover, common microencapsulated phase change materials have severalinherent problems, such as low thermal conductivity, big volume changeof the core PCM, the thermal and mechanical instability at pumping andhigh viscosity of concentrated slurry compositions, decreasing theirpumping efficiency.

The main shortcomings of the existing bulk ESM are low ability tomaintain the shape and mechanical properties (form stability) and theleakage of melted PCM during phase change process, which may be aproblem over a long period of material exploitation. These effects limitthe possible amount of PCM in the ESM (usually up to 10-30 w/w %), that,in turn, reduces the efficiency of thermal energy transfer system.

Some ESMs tend to solidify at the edges of the containers preventingeffective heat transfer. The common problems of the known shellmaterials have a scarce sealing tightness, endurance, elastic strength,water and fire resistance and high chemical reactivity. Much effort isstill needed to improve the performance ESM, such as specific heat,thermal conductivity and durability, and to understand the flow and heattransfer characteristics of slurries from encapsulated PCMs, so as topromote the applicability at the industrial scale.

The novel use of non-derivatized microcrystalline cellulose seems a verypromising material for use as a shell in microcapsulated ESMs both solidand fluidized, because of its excellent physical and chemical propertiesand biocompatibility, but up to now does not used in these applicationsbecause of great difficulties in microcrystalline cellulose dissolutionin the conventional solvents.

According to the invention cellulose/IL solution or cellulose hydrogelwere added to an agitated hydrocarbon dispersion in water(oil-in-water), or to water droplets dispersed in agitated hydrocarbon(water-in-oil), and stable dispersions were obtained without use of anyadditional surfactant. Therefore the invention includes a compositionconsisting water (oil-in-water), or water droplets dispersed in agitatedhydrocarbon (water-in-oil) and non-derivatized cellulose/IL solution ornon-derivatized cellulose hydrogel. Surprisingly, the invention providesthat the composition is free of a surfactant. Non-derivatized celluloseof the invention is, in some embodiments, in a crystal form.

Thus cellulose plays the role of a novel eco-friendly emulsifying agent.Surprisingly, for the duration of about a year neither reversible(flocculation) nor irreversible (coalescence) changes of dispersionshave been observed.

The solid-state dispersion, obtained by drying liquid dispersions ofnon-volatile compounds such as paraffin oil or eicosane, can berepeatedly dissolved in excess water to re-form a sustainabledispersion. Complete re-dispersion occurs in less than a minute undercommon agitation or sonication. The re-dispersion effect is not observedwith more volatile compounds such as heptane, which are lost duringdrying. This effect may be useful in application as self-emulsifyingdrug delivery systems. Attempts to extract the hydrocarbon within thesolid-state dispersion using polar organic solvents (ethyl ether,dichloromethane) have failed, indicating the integrity of a continuouscellulose barrier on the encapsulated hydrocarbon.

The invention provides, novel methods for encapsulation materials innon-derivatized cellulose shell which permits the fabrication ofvitamins isolated from the deteriorating effects of oxygen, retardingevaporation of a volatile core, improving the handling properties of asticky material, isolating a reactive core from chemical attack,controlled release of drugs or pesticides, masking the taste or odor ofthe core or increasing the selectivity of chromatography oradsorption/extraction processes. The invention provides, the use of thepresent compositions which include a non-derivatized celluloseshell/capsule in: adhesives, carbonless copy papers, e-papers or e-inks,scratch-n-sniffs, self-healing materials, environment adaptive textiles,visual indicators, etc.

The novel phase change materials, fabricated according to the presentinvention, can be directly used or consumed as a component of thecomposite-like energy storage materials in thermal energy storage andsustainable energy technologies and applications like solar energyutilization, energy conserving in buildings, thermal insulation, thermaladaptable textile materials, autonomous heat exchangers for the electricpower transformers, etc.

In some embodiments, solid ESMs are used as heat storage media forelectrical boiler to peak shift of electrical demands by storing heat atnight and releasing the heat in the daytime. Furthermore, there is muchwaste heat discharged from flue gas and water vapor at the phase changetemperature zone in industry. ESMs can absorb this heat for temporarystorage and can dissipate this heat for later use in its common phasechange temperature range of 40-90° C.

Encapsulated ESM can be readily dispersed into carrier fluids to formliquid ESM slurries, which can be used as both the heat transfer andenergy storage media, in particular for the secondary refrigeration orair conditioning loop systems.

The system with PCM can reduce the volume of the heat storage tankscompared to the system with water for heat storage. As is known, the ESMslurry is mainly made of PCM and water. So, in the phase changetemperature range of PCM, it not only store or release sensible heatwith the help of water contained in the slurry, but also latent heatwith the help of PCM contained in the ESM. Under the condition ofstoring the same amount of heat, the system with ESM can sufficientlyreduce the volume of the heat storage tanks.

The system with PCM can reduce pumping power consumption compared towater as heat transfer media due to latent heat. Compared to water forheat storage and transfer media, the PCM has larger heat storage densityand can reduce pumping power consumption in transportation.

Because of relatively high electroconductivity, the present novel ESMslurry is ready for use in electrical induction heating loops and couldbe easily pumped by use of magnetohydrodynamic pumps in compact thermalexchange systems, which are extremely economic, portable and reliablebecause of the absence of electric heating spirals and any solidrotation and friction parts, in particular in a closed-circuit portableheat exchange systems for automobile, airplane or rocket engines.

If oil and water are mixed and small oil droplets are formed anddispersed throughout the water, eventually the droplets will coalesce todecrease the amount of energy in the system. However, if small (100-1000nm) solid particles in form of powder are added to the mixture, theywill bind to the surface of the interface and prevent the droplets fromcoalescing thus causing the emulsion to be more stable. In thegeneralized form, in the two-phase system, consisting of two immiscibleliquids, the small solid particles can behave like molecules of surfaceactive substances—surfactants (typical molecular size <1 nm). This typeof emulsion was named after S. U. Pickering.

In some embodiments, properties such as hydrophobicity, shape, and sizeof the particle have an effect on the stability of the emulsion. Asprovided hereinabove, the particle's contact angle to the surface of thedroplet is a characteristic of the hydrophobicity. If the contact angleof the particle to the interface is low, the particle will be mostlywetted by the droplet and therefore will not be likely to preventcoalescence of the droplets. Particles that are partially hydrophobic(i.e. contact angle of approximately) 90° are better stabilizers becausethey are partially wettable by both liquids and therefore bind better tothe surface of the droplets. Generally the phase that preferentiallywets the particle will be the continuous phase in the emulsion system.

In some embodiments, adsorbing particles on the borders of droplets isnot reversible. The difference in the behavior of particles andsurfactants is due to the fact that molecules of surfactants have aseparated in space hydrophilic and hydrophobic parts, whereas thePickering particles have an isotropic surface. Therefore, small solidparticles cannot be packed in structures like micelles and they cannotbe amphiphilic. In some embodiments, a disadvantage of Pickeringemulsions is that they are susceptible to Ostwald ripening, wherebydiffusion through the continuous phase and between the droplets of thedisperse phase (because of gaps between Pickering particles) can lead toan increase in the median droplet diameter over time or evaporation ofthe droplet content. This increase in droplet diameter increases therate of separation of the disperse phase driven by densitydifferences—either sedimentation or cream formation due to buoyancy.Ultimately this ripening can render the product unfit for use becausefor example it requires re-homogenization, or because the droplets aretoo coarse to remain dispersed in the spray tank prior to application tothe target, or because the droplets are too large to give evendistribution of the active ingredient when applied to the target.

In some embodiments, non-derivatized microcrystalline or microfibrillarcrystal cellulose powder of the invention, being partially wetted byboth aqueous and oil phases, may adsorb at aqueous-oil interfaces and iscapable of stabilizing emulsions (Pickering effect). A densely packedmonolayer of cellulose particles or a three-dimensional network ofparticles of the present invention provides unexpected stability ofthese emulsions.

The cellulose particles remain at all time, in some embodiments, in aninitial microcrystal or fibrillar crystal form (before and afterformation of dispersions). This particles form interrupted mechanicalscaffolding barrier around dispersed material, which does nothermetically covers of the droplets. In one embodiment, this hermeticmolecular cellulose shell hinders the growth of the median dropletdiameter over time and/or evaporation of the volatile droplet content.

In some embodiments, the compositions of the invention comprise acovering material that comprises or consists a non-particulate andnon-crystal material—the cellulose of the invention. In someembodiments, the compositions of the invention are characterized byenveloping of droplets by continuous non-derivatized cellulose molecularlayer(s) (at least one layer) or cellulose molecular network, whichhermetically covers of the droplets.

In another embodiment, drying of the compositions of the inventionallows obtaining the reversibly dissolvable solid-state dispersions. Inanother embodiment, drying is drying at least 90% of the water or liquidcontent. In another embodiment, drying is drying at least 95% of thewater or liquid content. In another embodiment, drying is drying atleast 98% of the water or liquid content. In another embodiment, dryingis drying at least 99% of the water or liquid content.

In another embodiment, cellulose hydrogel capsules of the invention aresuspended in an aqueous liquid and used as surprisingly efficient mediumfor the enzymatic hydrolysis of cellulose to glucose. In anotherembodiment, provided herein a method for high-efficiency hydrolysis ofcellulose to glucose. In another embodiment, provided herein a methodfor high-efficiency production of bio-fuel (ethanol) by subsequentfermentation. In another embodiment, provided herein a method forincreasing cellulose enzymatic accessibility. In another embodiment,provided herein a method for overcoming cellulose hydrolysisrecalcitrance.

In another embodiment, cellulose hydrogel capsules of the inventionsuspended in an aqueous media, and comprising a cellulose hydrolyzingenzyme, provides enhancement of cellulose hydrolysis into glucose. Inanother embodiment, this efficiency is achieved due to a uniquecombination of five factors: (i) exceptionally high hydration of thecellulose hydrogel shell (liquid/cellulose weight ratio up to 99:1),(ii) full absence of crystallinity in cellulose hydrogel shell, (iii)exceedingly small cellulose shell thickness (less than 100 nm), (iv)high cellulose hydrogel porosity (about 3 cm/g) and (v) very highcellulose hydrogel shell specific surface area (more than 600 m²/g).

In another embodiment, cellulose hydrogel capsules comprising acellulose hydrolysis enzyme is provided in a phase-change material (PCM)as the oil embedded in the capsule (see Rein D M, Khalfin R and Cohen Y,J. Coll. Inter. Sci. 386, 456 (2012) which is hereby incorporated byreference in its entirety). In another embodiment, the PCM systemfurther promotes a beneficial spatial arrangement of the cellulosemolecular planes in the hydrogel shell that further enhance thehydrolyzing enzymatic activity.

In another embodiment, the phase change of the PCM oil within thecellulose coated capsules from liquid to crystalline phase, in thecooling stage of the dispersion process, provides and added beneficialeffect: the process of crystallization is accompanied by a reduction ofthe PCM core volume, thus the gap, formed between the cellulose hydrogelshell and the crystalline PCM core, is filled by the surrounding liquidwith the enzyme that penetrates into the particle gap through the porousshell. In another embodiment, the phase change of the PCM oil within thecellulose coated capsules allows additional increase of the enzymatichydrolysis caused by the optimal orientation of cellulose moleculesturned to the internal side of the PCM particle shell. In anotherembodiment, the phase change temperature range of the

PCM core material is specifically adjusted for optimum hydrolysisprocess.

Additional objects, advantages, and novel features of the presentinvention will become apparent to one ordinarily skilled in the art uponexamination of the following examples, which are not intended to belimiting. Additionally, each of the various embodiments and aspects ofthe present invention as delineated hereinabove and as claimed in theclaims section below finds experimental support in the followingexamples.

EXAMPLES

The cellulose shell encapsulation method represents a kind ofcoacervation process and consists from the several stages:

Cellulose Solution and Hydrogel Preparation

Initial solution was prepared by dissolution of different amounts ofcellulose microcrystalline powder (3-15 wt. %) in the EMIMAc, pre-heatedin the water bath to about 85° C. A magnetic stirrer was applied to thesolution up to full cellulose dissolution during less than 10 min. Itwas found that practically instantaneous uniform dissolution can beachieved by impregnating the cellulose batch with the small amount of ahighly volatile diluent (for example, dichloromethane). To limitcellulose decomposition due to the high exothermic effect accompanyingthe dissolution process, the solution temperature should not exceed 120°C. Cellulose hydrogel was prepared by immersing the solution under mildstirring in a water coagulation bath at room temperature for about 5min. The regenerated cellulose hydrogel was washed thoroughly withdeionized water.

Prior to cellulose dissolution in the ionic liquid, the crystallinepowder was impregnated with a small amount of volatile liquid. Severalliquids were evaluated: acetone, chloroform, diethyl ether,acetonitrile, and pyridine. Results were approximately the same, andthus we chose dichloromethane (T_(boil)=40° C.), which can be evaporatedfrom the reaction zone fully and rapidly, without “explosive boiling” inthe context of our experiments.

Preparation of Hydrocarbon Dispersion in Cellulose Solution

Features of ultrasonic emulsification: the process of ultrasonicemulsification commences when a certain intensity of irradiation isattained, this intensity being the cavitation threshold. The rate ofemulsification increases with increasing irradiation intensity anddecreasing liquid viscosity. For any intensity, there is a correspondingmaximum concentration of emulsion that can be produced; this limitingconcentration increases with increasing intensity. Its existence isascribed to the attainment of an equilibrium state between the twoconflicting processes of emulsification and coagulation. An increase intemperature reduces the emulsification efficiency because of anincreasing trend toward coagulation. The size of the particlesconstituting the dispersed phase is dependent on the acoustic intensityand the time of irradiation. [E. Webster, Ultrasonics 1 (1963) 39]. Inthe preliminary experiments it was found that to effectively overcomethe cavitation threshold in our experimental conditions, it wasnecessary to expose the investigated solutions of 20 or 50 mL to sonicpower of about 130 or 310 W, respectively, for a duration of about 10min at temperature of about 110° C. Easier and more uniform ultrasoniccavitation promotes by existence of gaseous traces of dichloromethane inthe mixture.

A batch of hydrocarbon, either as crushed solid, melt or solution inDCM, was introduced directly into the heated cellulose/IL solution. Theobtained mixture was subjected to the ultrasonic emulsification by thetip sonicator. At elevated viscosities, when the celluloseconcentrations exceeds 10 wt. %, small amounts of diluent (1 wt. %),such as acetonitrile or pyridine, was added to the solution to reduceits viscosity. In order that the entire volume of processed liquid isinvolved in the ultrasonic cavitation, the sonicator's tip wascontinually moved across the boundary between the IL solution and thehydrocarbon up to complete disappearance of boundary.

Hydrocarbon Encapsulation in the Cellulose/IL Solution

Coacervation was induced by adding excess deionized water to thesonicated mixture (about 4:1 volume ratio). Water temperature could beeither above or below the phase transition temperature of the corematerial (for eicosane the suitable range is 20-70° C.).

Preparation of Dispersions Using Cellulose Hydrogel

Cellulose hydrogel pieces were added at ambient conditions to theagitated hydrocarbon dispersion in water (oil-in-water), or to waterdroplets dispersed in agitated hydrocarbon (water-in-oil) withsubsequent sonication for 10 min. About 4 g of hydrogel containing 5 wt.% of cellulose were added per 1 g of hydrocarbon or water, to obtain astable oil-in-water or water-in-oil dispersion, respectively.

Thickening and Drying of the Obtained Liquid Dispersion

The hydrocarbon/cellulose dispersion in the IL/water solution wassubjected to dialysis against pure water for 24 hours. This enabledexchange of EMIMAc with water in controlled manner (details provided insupplemental information). IL-free aqueous dispersions were thusobtained either as described above or by the direct use of the cellulosehydrogel as emulsifier. These were further dialyzed against 20 wt. %aqueous PEG solution at ambient temperature for 24 hours, followed byoven desiccation for 4 hours at 60° C. to yield a so-called “solid-statedispersion.

Electroconductivity of hydrocarbon/cellulose water/IL dispersions: inorder to estimate the necessary duration of the dialysis process of thecellulose/IL solutions against pure water, different times andtemperatures of dialysis were investigated. Variation of theseparameters yields dispersions with different IL content in the waterand, as a result, with different electrical conductivities. Experimentalresults are shown in FIG. 1, electroconductivity was measured with aPrecision Impedance Analyzer Agilent 4294A (Agilent Technologies Co.,USA) at 0.5 V and 10 kHz. It is observable that the electricalconductivity of a dispersion dramatically increases with water contentup to a maximum at a ratio of water to cellulose/IL dispersion of 1:2,and then decreases. The increase in the electrical conductivity from thevalue of the pure IL based dispersion to the value at the maximum isabout 13 times. A peak in the conductivity also appears for the majorityof concentrated electrolyte solutions. [P. Claes, Y Loix, J. Glibert,Electrochim. Acta, 28 (1983) 421] This effect could be explained by thepresence of two multidirectional mechanisms. One of them is the numberof ions present to transport charge (which induces conductivity toincrease with the IL concentration). The other one is related with themobility of the ions in the solution, which will be lower when thenumber of ions increases (and so it induces conductivity to decreasewith concentration). [J. Vila, P. Gines, E. Rilo, O. Cabeza, L. M.Varela, Fluid Phase Equilibria 247 (2006) 32] Data on changes of theelectrical conductivity of dispersion in the dialysis permit estimationof the speed of dispersion dilution and confirms the nearly completeimplementation of the dialysis process at room temperature through aboutof 24 hours.

Blowing of the Concentrated Precipitate

A different drying process of the IL-free aqueous dispersions wascarried out in a rotary evaporator or vacuum oven (at about 35° C. and0.67 kPa). In this case, blowing of concentrate occurred at the finalstage of drying yielding a foam-like solid-state dispersion. As a corematerials for encapsulation could be used a paraffins (alkanes) or fattyacids.

As an ionic liquid solvent for cellulose could be used1-ethyl-3-methylimidazolium acetate (EMIMAc) or1-butyl-3-methylimidazolium chloride, etc.

As a cellulose non-solvent could be used water, alcohols, ketones,chlorinated alkanes, etc.

N-Eicosane, with a purity of above 98% was supplied by Merk, Germany.Microcrystalline cellulose powder with particle size in range 20-160.mu.m and EMIMAc of 90% purity were supplied by Sigma-Aldrich Co. EMIMAcand cellulose were dried in a vacuum oven at 60° C. at 0.26 kPa for atleast 24 hours. Polyethylene glycol (PEG, M_(w)=20,000), light paraffinoil (mixture of saturated hydrocarbons with an average chain length of11 carbon atoms), dichloromethane (DCM), ethyl ether, acetonitrile,pyridine and heptane were purchased from Sigma-Aldrich Chemicals. Thesechemicals were used without additional purification. Unless otherwisestated, the percentages of the components were calculated based on thetotal composition of the final mixture.

Equipment and Characterization Methods

Emulsification of the dispersions was performed using an Ultrasonic celldisrupter 2000U (Ultrasonic Power Corp., USA) equipped with finger-liketip. The morphology of the form-stable blends was investigated by a highresolution scanning electron microscope (HR-SEM) Ultra Plus Gemini(Zeiss Co., Germany) and cryogenic transmission electron microscope(cryo-TEM) T12G² (FEI Co., Netherlands). Vitrified samples for cryo-TEMwere prepared in a controlled environment vitrification system (CEVS) atcontrolled temperatures (either 25 or 60° C.) and 100% relativehumidity. A droplet of the dispersion was placed on the TEM grid coveredby a holey carbon film and blotted from the back side to yield a thinliquid film spanning the holes. The sample was vitrified by plunginginto supercooled liquid ethane. The specimen transfer to the microscopewas done using an Oxford Instruments CT-3500 cryo-specimen coolingholder and transfer procedure. The samples were investigated using lowdose electron imaging and acceleration voltage of 120 kV. Images wererecorded using Gatan 791 MultiScan CCD camera and the image processingwas done by Gatan Digital Micrograph 3.9.2 software package. AMastersizer 2000 instrument (Malvern Co. Ltd., UK) was used to measurethe particle size and distribution. Zeta-potentials of the dispersionswere measured with a Zetasizer NanoZS instrument (Malvern Co. Ltd., UK),equipped with a He—Ne red light laser of 633 nm wavelength.

For the dialysis processes we used Spectra/Por® molecular porousmembrane tubes (MWCO 12000-14000, volume/length=2 mL/cm, SpectrumLaboratories, Inc., USA).

The DSC measurements were realized on Mettler Toledo DSC 1(Mettler-Toledo, Inc., USA) in temperature interval 5-100° C. atscanning rate: 10° C./min. TGA measurements were performed on TAQ5000-0486 Thermal Gravimetric Analyzer (TA Instruments Inc., USA), intemperature interval 20-370° C., at heating rate of 20° C./min.

X-ray diffractometry of the samples was performed on small/wide-anglediffractometer (Molecular Metrology SAXS system) equipped with a sealedmicrofocus tube (MicroMax-002+S) emitting Cu Kα radiation (λ=0.1542 nm).

EXAMPLES Example 1 Preparation of Cellulose Solution

Initial solution was prepared by dissolution of cellulosemicrocrystalline powder (3-15 wt. %) in the preliminary heated EMIMAc(70-90° C.) using magnet stirrer during 10-20 min. For quicker and moreuniform dissolution, the batch of cellulose could be preliminary“diluted” by the stirring in highly volatile diluent—dichloromethane inthe weight ratio of 1 part of cellulose to 3 parts of liquid. It havebeen checked several liquids: acetone, chloroform, diethyl ether,acetonitrile, pyridine with the approximately same success, and, as aresult, stopped our choice on dichloromethane, T_(boil)=40° C., whichcan be evaporate fully and rapidly, but without the “explosive boiling”in the context of our experiments.

Example 2 Preparation of Alkane Dispersion in Cellulose Solution

As a samples of alkanes were used heptane (C₇H₁₆), light paraffin oiland n-eicosane (C₂₀H₄₂).

First Variant.

The necessary batch of alkane could be introduced directly (in the solidor molten form) into the ready cellulose/IL solution or preliminarydissolved into aforesaid diluent liquid (if this is possible) beforestirring with cellulose powder. As we use the dichloromethane, which isan excellent solvent for alkanes, we prepared the solutions of alkanesin weight ratio between alkanes and cellulose from 1:1 to 5:1. Preparedsolution was poured into preliminary heated cellulose/IL solution. Theobtained mixture was immediately subjected to the ultrasonicemulsification.

Second Variant.

Cellulose hydrogel pieces were added at ambient conditions to theagitated hydrocarbon dispersion in water. The obtained mixture wasimmediately subjected to the ultrasonic emulsification.

The process of ultrasonic emulsification commences when a certainintensity of irradiation is attained, this intensity being thecavitation threshold. The rate of emulsification increases withincreasing intensity. For any intensity, there is a correspondingmaximum concentration of emulsion that can be produced; this limitingconcentration increases with increasing intensity. Its existence isascribed to the attainment of an equilibrium state between the twoconflicting processes of emulsification and coagulation. The frequencymay also determine which of the two liquids becomes a disperse phase.Highly viscous liquids (more than about 0.2 Pas) do not readily emulsifydue to big difference in the levels of the absorption of acoustic powerone of liquids compared to other one, and an increase in temperaturereduces the emulsification efficiency because of an increasing trendtoward coagulation. Evidence of the dependence of ultrasonicemulsification is contained in the fact that it is impossible toemulsify degassed liquids: the emulsifying threshold decreases withincreasing dissolved gases content. The size of the particlesconstituting the disperse phase is dependent on the acoustic intensityand the time of irradiation.

The initial properties of the 7.5 wt. % cellulose/IL solution heated to50-90° C. was found acceptable for the efficient ultrasonicemulsification. In our experiments was found that for the 20 mL of theinvestigated liquid the optimum sonic power (determined by equilibriumbetween emulsification and coagulation processes) is about 130 W and for50 mL is about 310 W during 5 min. Existence of gaseous traces ofdichloromethane in the mixture promotes the ultrasonic cavitation. Atlower temperatures the viscosity of solutions could be reduced byaddition of small amounts of diluent, such as acetonitrile or pyridine.

Example 3 Coacervation of Joint Alkane/Cellulose Mixture

A complex coacervation of prepared joint alkane/cellulose mixture by itscoagulation with excess of deionized water (about 20 mL of water per 20mL of initial alkane/cellulose mixture was prepared; water temperaturewas 25-80° C.). As a result of complex coacervation process was obtainedthe milk-color suspension.

Obtained suspension was subjected to dialysis against pure water or 20wt. % water solution of polyethylene glycol (M_(w)=20000) at roomtemperature during 8 hours and/or vacuum oven drying during 24 hours at60° C.

Example 4 Properties of the Novel Cellulose Shell Encapsulated ThermalEnergy Storage Materials

As a result of the aforesaid procedures were obtained and investigatedseveral samples of novel cellulose shell encapsulated thermal energystorage materials. In the samples, described below, the n-eicosane wasused as a PCM material.

Sample 1.

Liquid suspension consists of 10 wt. % of cellulose encapsulated PSM inIL/water diluent (1:1 v/v), obtained according to method and procedure,discovered above.

Sample 2.

Liquid suspension consists of cellulose encapsulated PSM in pure waterdiluent after dialysis of initial suspension (as in sample 1) andfollowing vacuum drying up to PCM/cellulose capsules content of 10, 20,30 and 45 wt. %.

Sample 3.

Dry solid ESM, obtained after dialysis of initial suspension againstpure water and vacuum drying of the material as in sample 2.

The below tables indicate the measured physical properties of thesamples:

Parameters Heat of Heat of melting, J/g crystallization, Particle (vs.slurry J/g (vs. slurry concentration concentration in concentration inSample in diluent, water, wt. %) water, wt. %) number wt. % 10 20 30 4510 20 30 45 1  10  25  29 2 10 20 30 45 25 45 75 101 27 48 77 105 3 100225 229

Parameters Subcooling Freezing and Electrical Average temperaturesuperheating conductivity Encap- particle Sample of slurry, of core, ofslurry, sulation diameter, number ° C. ° C. S/m ratio, % nm 1 −20 <1 4.382 650 2 ~0 <2 ~0.08 78 200 3 — <1 — 80 ~300

Parameters Viscosity, Viscosity of mPa · s mixture (v/v) (vs. slurryconcentration sample 1:sample Sample in water, wt. %) 2 = 4:5 number 1020 30 45 mPa · s 1 21.6 0.8 2 1.2 1.6 7.5 30.4 3 — —

Parameters Accelerated thermal Thermal Melting cycling test Sampleconductivity, Redilution by temperature (3000 heat/ number W/(m · K)water of core, ° C. cool cycles) 1 0.5 possible ~37 pass 2 ~0.6 possible37-39 pass 3 0.25 possible ~37 passFormation of Cellulose Coated Oil-in-Water and Water-in-Oil Dispersions

When the cellulose/IL solution or cellulose hydrogel were added to theagitated hydrocarbon dispersion in water (oil-in-water), or to waterdroplets dispersed in agitated hydrocarbon (water-in-oil), stabledispersions were obtained without use of any additional surfactant (FIG.5a ). The control experiments, i.e. physical mixtures of cellulose/ILsolution and water as well as hydrocarbons/IL dispersion and water, didnot yield any stable dispersion but exhibited coagulated cellulosehydrogel in the first case, or instantaneous phase separation in thesecond. We interpret the dispersion stability as due to the amphiphiliccharacter of cellulose. This indicates that the macromolecules has beensuccessfully exfoliated from their crystal structure, so as to presentthe hydrophilic hydroxyl groups to water, and the more hydrophobicplanes of glucopyranose rings towards the hydrocarbon. Thus celluloseplays the role of a novel eco-friendly emulsifying agent. For theduration of about a year neither reversible (flocculation) norirreversible (coalescence) changes of dispersions have been observed inthe oil-in-water dispersions. Water-in-oil dispersions were somewhatless stable, and phase separation is observed after several months.

The solid-state dispersion, obtained by drying liquid dispersions ofnon-volatile compounds such as paraffin oil or eicosane, can berepeatedly dissolved in excess water to re-form a sustainabledispersion. Complete re-dispersion occurs in less than a minute undercommon agitation or sonication. The re-dispersion effect is not observedwith more volatile compounds such as heptane, which are lost duringdrying. This effect may be useful in application as self-emulsifyingdrug delivery systems. Attempts to extract the hydrocarbon within thesolid-state dispersion using polar organic solvents (ethyl ether,dichloromethane) have failed, indicating the integrity of a continuouscellulose barrier on the encapsulated hydrocarbon.

The particle size distribution of the representative cellulose coatedeicosane dispersion (eicosane/cellulose ratio 4:1) in water is shown inFIG. 6. It exhibits a trimodal distribution, peaked around 200, 550 and20,000 nm. This may be due to non-optimized method of preparation,possibly resulting in non-uniform sonic energy distribution in the smallvessel. No noticeable difference in the particle size distribution wasobserved after two weeks. The particle size distribution in there-dissolved dispersion obtained by magnetic stirring with water differsfrom that of the original one, exhibiting larger particles size.Additional sonication reduces this difference.

Microcapsules Morphology

Cryo-TEM images of vitrified thin films of the aqueous dispersions areshown in FIGS. 7 and 8. The images show mostly isolated particles about200 nm in diameter, as given by the main (first) peak of the particlesize distribution. It should be noted that cryo-TEM imaging requires athin film which prohibits observation of the larger particles. Theparticles mostly seem to have a uniform structure, with a rather smoothsurface. Agglomerates of smaller particles are not observed, nor aresmall particles observed on the surface, as would be in the case ofPickering emulsions. The particles containing paraffin oil and heptane,exhibited a globular shape and a homogeneous surface (FIG. 7b,c ).Eicosane-containing particles vitrified from 60° C., above its meltingtransition, exhibited a similar structure (FIG. 7a ), whereas thosevitrified after core crystallization (at ambient temperature) exhibitpronounced edges, following the contours of the crystal within them(FIG. 8), which exists in a triclinic crystal structure. The cryo-TEMimage of the vitrified dispersions where taken at minimal electrondosage. When the sample is exposed to enhanced electron irradiation, asin FIG. 8b (3000 e/nm²), noticeable radiation damage is observed in thedispersed oil. This is a well-known phenomenon due to water radiolysisforming radicals that degrade the hydrocarbons. Interestingly, a thinstable coating is observed and interpreted as the encapsulatingcellulose shell, which may have significant water content (cellulosehydrogel).

The morphology of the dried dispersions was investigated by HR-SEMimaging of the cryo-fractured surface. The fracture surface of theeicosane based sample is shown in FIG. 9. Microcapsules could becharacterized by a smooth surface. They form a very condensedagglomerate structure without visible boundaries between the particles.The dispersed particles appear to be completely covered by the celluloseshell. In cases where the fracture cut across the particles (inset inFIG. 10), no trace of the encapsulated hydrocarbon could be observed inthe broken capsules, which indicates poor adhesion between the core andits cellulosic shell. It also indicates that the cellulose shellthickness is less than 50 nm.

Morphology and Properties of the Blown Microcapsules

As mentioned above, drying the dispersion under reduced pressure caninduce blowing at the final stage of drying yielding a nanoporous foam(aerocellulose). The blowing agent can be either the residual water, orthe entrapped hydrocarbon if volatile. It is well known thatnon-derivatized cellulose hydrogel simply shrinks during drying and doesnot exhibit any blowing effects. The ease of the blowing process in thepresent case is related to the presence of the encapsulated hydrophobicmaterial. Apparently it induced the formation of the cellulose hydrogelshell which encases it, possibly with some trapped water. The blowing ofthese capsules under reduced pressure at the last stage of dryingresults in the observed structures, as shown in FIG. 10a . A much moreclearly defined cellular structure is observed when a volatilehydrocarbon is used, as shown for the case of heptane in FIG. 10 b.

Z-Potential and Chemical (pH) Stability of Dispersion

FIG. 11 shows the pH dependence of the ζ-potential of cellulose coatedeicosane dispersions. It very slow changes in the range of −1/−5 mV,within the investigated pH interval of 2 to 13. This weak changing lowvalue of the ζ-potential indicates that the particles are uncharged,thus the dispersion stability is not due to electrostatic repulsion.Therefore, one can conclude that the obtained very high stability ofthis dispersion is determined by the kinetic and hydration causes. Forcomparison, the ζ-potential of paraffin dispersions prepared with sodiumdodecyl sulfate as surfactant, has significantly negative value (about−60 mV) in the same pH range.

Calorimetric Analysis of Solid and Liquid Eicosane/Cellulose Dispersions

There is significant current interest in eicosane-based phase changematerials for storage of thermal energy, due to its high latent heat,transitions temperature in a practical range of interest, and low cost.FIG. 12 presents results of differential scanning calorimetry (DSC)measurements on solid eicosane/cellulose (4:1) dispersions and 6 wt. %aqueous suspensions re-dispersed from them. The effectiveheat-absorption capacities of the solid dispersion and re-dispersedaqueous suspension are about 65% and 7% relative to pure eicosane,respectively. Thus, an effective heat-absorption capacity of even a 6%aqueous dispersion of eicosane in temperature range of 35-45° C. is 4times greater than that of pure water. FIG. 13 shows thethermo-gravimetric analysis (TGA) and differential TGA (DTG) of thesolid eicosane/cellulose (4:1) microcapsules. Initial DTG peaks between50 and 160° C., corresponds to a mass loss of absorbed moisture ofapproximately 15%. The peaks in range of 180-320° C. (mass loss 70%) canbe attributed to oxidation of the eicosane and degradation of the ILtraces. The decomposition peak at about 350° C. can be attributed todecomposition and oxidative degradation of cellulose (mass loss 15%).These results indicate the good thermal stability of theeicosane/cellulose microcapsulated dispersion.

X-Ray Diffractometry

X-ray diffraction was used to investigate the crystalline features ofthe different components in the dried dispersions of eicosane/cellulose(4:1). The main features in the diffraction from the dried dispersion(line 3 in FIG. 14a ) are due to the crystal packing of eicosane atambient temperature, as shown in line 1 of FIG. 14a . This pattern issimilar to that of pure eicosane crystallized from the melt, and doesnot exhibit the characteristic diffraction pattern of cellulose crystals(I or II types). Line 2 in FIG. 14a displays the diffraction from thesame system heated to 60° C., above the melting temperature of eicosane.It displays a single broad maximum at about 20° which is due both to theamorphous halo of liquid eicosane and of amorphous cellulose (seesupplementary material). Subtracting of the diffraction from the molteneicosane from that of the dried dispersion at the same temperature (60°C.) yields a residual halo very similar to that of amorphous celluloseobtained by milling the crystalline form, and is also similar to thatobtained from the dried cellulose hydrogel obtained as described above,shown in line 4 of FIG. 14a . The insignificant cellulose crystallinityis in accord with the molecular-level arrangement of the cellulosemacromolecules so that their hydrophilic parts turn to water and thehydrophobic parts towards the hydrophobic hydrocarbon. X-ray diffractionthus indicates that this amorphous state exists both in the regeneratedcellulose hydrogel as well as in the cellulose-stabilized hydrocarbondispersions, and is most likely due to the effect of the ionic liquid inunraveling the microfibrillar cellulose crystals.

An interesting observation can be seen in the small-angle diffractionpatterns shown in FIGS. 14b and c . The sharp (002) reflection of theeicosane triclinic crystal in the bulk phase appears to have a weaksatellite at somewhat smaller angles. This resembles the reportedobservation in graphite-intercalated eicosane, where it was assigned asthe (02) reflection of an adsorbed phase exhibiting only two-dimensionallattice order. We suggest a similar interpretation in the present case,whereby the inner surface of the cellulose encapsulating layer interactswith adjacent eicosane molecules to induce the adsorbed phase.Surprisingly, the patterns from native and re-dissolved dispersionsexhibit reflections from both types of crystals, but now with aboutcomparable intensity. This indicates less-ordered packing of eicosanemolecules in the encapsulated particles compared to the bulk phase,which is apparently due to the influence of the encapsulating cellulose.SAXS patterns measured from the eicosane/cellulose dispersion uponheating in the temperature range of 30 to 50° C., at steps of 5° C.,indicate that both the triclinic bulk phase of the eicosane and theadsorbed phase melt together at about 37° C. This differs from theobservations of n-alkanes in graphite, where the disordered phase wasstable to significantly higher temperatures, and may be attributed tothe weaker interaction between eicosane and the cellulose shell (seeFIGS. 2-4).

Conclusions

The amphiphilic character of the cellulose chain can be exploited forformation of stable oil-in-water or water-in-oil dispersions. This maybe done by mixing water, oil and cellulose solution in an ionic liquid.A more practical alternative is to form first a hydrogel from thecellulose/IL solution by coagulation with water and applying it to thesonicated water/oil or oil/water mixtures. We postulate that thedissolution/regeneration process affords higher mobility to thecellulose molecules so an encapsulating coating can be formed at thewater-oil interface. Thus cellulose, due to its amphiphilic character,plays the role of a novel eco-friendly emulsifying agent. The dispersedparticles described here exhibit a globular shape and dimensions around200 nm for the main particle population, with some higher populations oraggregates. A solid-state dispersion is obtained by drying liquiddispersions of non-volatile compounds, and can be repeatedly dissolvedin excess water to re-form a sustainable dispersion. At the final stageof drying, under reduced pressure, the dispersion can be blown, yieldinga nanoporous foam (aerocellulose). The blowing agent can be either theresidual water, or the entrapped hydrocarbon if volatile. Thesolid-state eicosane/cellulose dispersion as well as the aqueousdispersions possesses a very high effective heat-absorption capacity.X-ray diffraction patterns indicate that the encapsulating celluloseshell is indeed in the amorphous state. Small-angle diffraction patternsof eicosane dispersions exhibit two sharp reflections. One is due to theeicosane triclinic crystal bulk phase and the other at somewhat smallerangles is interpreted as due to less ordered phase, possibly due tointeractions with the encapsulating cellulose.

Example 5 Enzymatic Hydrolysis of the Novel Cellulose Hydrogel Capsules

Solid-state dispersion included 10 wt. % of cellulose encapsulatedneicosane (obtained according to method and procedure, discovered above)and was dissolved in water based acetic buffer (at 25° C.) withconcentration of 50 mmol/L (pH˜4.8) at weight ratio of 1:5.

The prepared dispersion was mixed at room temperature with a blend ofcommercial cellulolytic enzyme GC-220 (Genencor In., Danisco, N.Y., USA)and b-glucosidase Novozyme-188 (Novozymes A/S, Bagsvaerd, Denmark). Theloading of GC-220 was 10 FPU per 1 g of pure cellulose and Novozyme-188was 8 IU per 1 g of pure cellulose.

The kinetics of the cellulose hydrolysis were measured according tochanges of the glucose concentration in the solution (which was testedby the conventional DNS-assay). The comparison with the hydrolysiskinetics of standard microcrystalline cellulose (Avicel, Sigma-AldrichLtd.) dispersion in the same enzymatic mixture showed more thanhundredfold increase in hydrolysis speed of the present cellulosehydrogel capsules.

Example 6 Enzymatic Hydrolysis Properties of the Novel CelluloseHydrogel Shell Encapsulated PCM Materials

Liquid suspension included 10 wt. % of cellulose hydrogel encapsulatedPCM based on n-eicosane core (obtained according to method and procedureas provided hereinabove) in water based acetic buffer with concentrationof 50 mmol/L (pH˜4.8) and was mixed with enzymatic blend as described inExample 5 at 55° C.

The suspension was quickly cooled to the surrounding temperature (25°C.) and measurement of cellulose hydrolysis kinetics was realized asdescribed in Example 5. The comparison with the hydrolysis kinetics ofstandard microcrystalline cellulose dispersion in the same enzymaticmixture had shown more than 130-times increase of hydrolysis speed infavor of the present cellulose hydrogel encapsulated PCM.

The invention claimed is:
 1. A method for making an oil-in-waterdispersion or water-in-oil dispersion, comprising the step of mixing ahydrophilic medium, a hydrophobic composition and non-derivatizedcellulose solution in an ionic liquid; wherein said oil-in-waterdispersion or said water-in-oil dispersion is in the form of one or moreparticles; and wherein said mixing is mixing in the absence of asurfactant.
 2. The method of claim 1, wherein said non-derivatizedcellulose solution is a hydrogel.
 3. The method of claim 2, wherein saidhydrogel is formed by coagulating a cellulose/IL solution with water. 4.The method of claim 1, wherein said non-derivatized cellulose is anemulsifying agent.
 5. The method of claim 1, further comprising drying asolid-state dispersion of the oil-in-water dispersion or thewater-in-oil dispersion thereby conserving said solid-state dispersion.6. The method of claim 1, further comprising a subsequent fermentingstep, thereby obtaining biofuel.